1. Field of the Invention
The invention is related to the power supply with the function of the power transform adjustment, particularly for the automatic outer loading detection and additional feedback control to provide the output current and charging period according to the different of the dual-slope power supply.
2. Description of the Prior Art
Regarding the prior art for the dual-slope power controller, the related technology has described the power supply, wherein the output voltage is detected, fed back to the internal detection circuit, compared to internal reference voltage, and generates an error voltage, for which the transformer generates different current driving slope, period and pulse width modulation control signal, finally obtain the control effect for the output driving current.
As shown in FIG. 1, a known power supply control circuit comprises a power transformer 4, a feedback control circuit 8 and an outer loading device 6, wherein the power transformer 4 accepts its input voltage Vin and provides an output voltage Vo to the loading device, and the feedback control circuit 8 output a gate pulse according to the output voltage Vo level, which provides different voltage level through the voltage transformer. When the output loading device 6 is in the larger loading, the feedback control circuit will provides a large gate pulse; otherwise when the output loading device 6 is in smaller loading, the feedback control circuit 8 will provide smaller gate pulse, where the power transformer 4 provides small power output and eliminates the power consumption. Generally, the power transformer 4 can adopt Buck converter, Boost converter, Fly-back Converter, or other different transform controller according to different requirements. Besides, the design of the feedback control circuit 8 majorly adopts pulse width modulation to adjust the control method for the power transformer. Therefore, it is more important for the design of the feedback control circuit 8 to determine the output gate pulse according to the loading status of the outer loading device 6, and the power transformer 4 providing suitable output power to the outer loading device 6.
Refer to FIG. 2, it is the control circuit for the output gate pulse of the feedback control circuit 8 in the previous technology. As shown in FIG. 2, the voltage transform circuit utilizes the input error voltage Ve to control the charging-discharging current value of the storage capacitor 25, and further control the rising-falling period for the capacitor voltage Vramp to achieve the purpose of the gate pulse control. The control circuit includes four current sources, which are the first charging current source 21, the first discharging current source 22, the second charging current source 23, and the second discharging current source, and four set current control switches, which are the first switch 211, the second switch 221, the third switch 231, and the fourth switch 241, and the storage capacitor 25, the controller 26, the charging and discharging circuit 27 and the transform circuit 28, in which the storage capacitor 25 is used to provide the function of charge and discharge. Besides, the first charge current source 21 is connected to the storage capacitor 25 through the first switch 211; the first discharge current source 22 is connected to the storage capacitor 25 through the second switch 221; the second charge current source 23 is connected to the storage capacitor 25 through the third switch 231; the second discharge current source 24 is connected to the storage capacitor 25 through the fourth switch 241; the transform circuit 28 generates an output transform control signal according to the voltage transformation of the error voltage Ve, to adjust the drain current of the second charge current source 23, and output a reset signal (Reset) to the corresponding switch (SW1˜SW4) according to the voltage of the switching current CS. The controller 26 has the inputs of the capacitor voltage (Vramp), a high reference voltage level (VH), a low reference voltage level (VL), an output control signal (first and second control signal), an output pulse (CLKOUT), and utilizes the control signal to determine the charge-discharge current value of the charge-discharge storage capacitor 25, the period of the capacitor voltage (Vramp) and the frequency of the gate pulse by the control of the first charge current source 21, the first discharge current source 22, the second charge current source 23, and the second discharge current source 24.